1. Field of the Invention
The present invention relates generally to a method for automatically inspecting an object and to an apparatus for performing the method, and more particularly to an automatic inspection method and apparatus for determining defects in products or components by the use of an optical image sensor rather than by measurement of absolute dimensions or the like.
2. Description of the Prior Art
Various types of automatic inspection devices have been proposed and utilized to replace the visual inspection of products or components by a human inspector. Conventional devices use optical image sensors such as, for instance, a television camera to photosense the products or components and then by processing the image signals therefrom in a data processor such as a computer or the like, determine the shape, dimension, surface defects, etc. of the product.
Several examples of the automatic inspection devices according to the conventional art will be explained with reference to FIGS. 1, 2, and 3. In the example of FIG. 1, 1 designates a television camera, 2 an electronic processor such as a computer or the like which processes the video signals from the television camera 1; 3 and 3A, respectively, designate light sources for illuminating purposes; 4, 4A, 5 and 5A reflection mirrors; 7 and object to be inspected such as products or components, and 6 a standard body for the object to be inspected that has no defects. The images of the standard body 6 and of the object 7 being inspected, as illuminated by light sources 3, 3A respectively, are received by the television camera 1 being introduced therein in overlapping relationship brought about by the combinations of reflection mirrors 4, 4A and 5, 5A, respectively. If the shape or patterns of the standard body 6 and inspected object 7 are entirely coincident with each other, the inspected object 7 is deemed to be good and the processor 2 does not deliver any output signal, but if there is a difference between the two, even in one part, the inspected object 7 is deemed to have a defect and the processor 2 delivers a defect signal.
In other words, the conventional example shown on FIG. 1 constitutes an inspection method where the standard object 6 and the inspected object 7 are placed at separate locations while they are illuminated with separate light sources, respectively. The two images are overlapped by utilizing the mirrors, and they are inspected by determining whether the two images are matched or not.
In the other conventional example as shown on FIG. 2, it is assumed that the object 7 to be inspected has a pattern which consists of a black coloured portion 7A and a transparent portion 7B, whereas a standard object 8 has a standard pattern such as a negative picture against the inspected object 7 which is a pattern that is opposite the black portion 8A and transparent portion 8B to the inspected object 7. In FIG. 2, 9 designates a reflection mirror that is located at the opposite side of the standard object 8, from the object 7 being inspected. In this case, the inspected object 7 and standard object 8 are arranged so that they are on the same axis to the optical axis of the television camera 1, which is itself located at the side of the inspected object 7 and that the standard object 8 keeps its standard pattern in a faithful positive to negative relation against the inspected object 7. In such case, if the pattern of the inspected object 7 shows a truly positive to negative relation to the negative standard pattern of the standard object 8 (if there are not defects), the light from the light source 3 which is placed between the camera and the object 7 does not pass both patterns and is not reflected by reflector 9 and hence does not enter the television camera 1. However, if there is a defect in the pattern of the object 7, the light will reach the reflection plate 9 through the defect and then be reflected to the television camera 1 so that the processor 2 that receives the video signal therefrom will judge that there is a defect and thereby deliver a defect signal.
Further, as another example of the prior art, as shown in FIG. 3, there is a method in practice that judges the good or bad of the inspected object 7 by comparing the pattern of the inspected object 7 as photosensed by television camera 1 or the like with a memorized standard pattern as readily stored in the memory of the computer 2A that is used as the processor.
As will be understood from the first and second examples as described above, both conventional defect inspection methods require some kind of a standard subject against which the inspected object is to be compared. In the third example, as shown on FIG. 3, a pattern of the standard object is memorized in the memory of the computer which pattern is to be compared to the pattern from television camera 1, as it picks up the inspected object. Therefore, the requirement of a standard pattern cannot be disregarded for this third case.